California Governor Gavin Newsom has declared a state of emergency in Orange County over a massive chemical tank that is poised 'spill or explode.'

More than 40,000 residents were evacuated on Saturday after emergency crews failed to neutralize the 34,000-gallon tank at a GKN Aerospace facility in Garden Grove.

The tank contains highly volatile methyl methacrylate (MMA) which officials fear could leak out or explode, possibly triggering a toxic chain reaction in other nearby containers.

'The safety of Orange County residents is the top priority,' Newsom said in a statement. 

'We are mobilizing every state resource available to support local responders and make sure the community has what they need to stay safe.'

If the problem cannot be secured, officials said an explosion could damage adjacent buildings, start a fire or dump 6,000 to 7,000 gallons of 'very bad chemicals.'

'California's Office of Emergency Services continues to work alongside our local partners to support the ongoing hazardous materials response operation,' said Director Caroline Thomas Jacobs in the joint statement. 

'Our role is to coordinate resources, share critical information, and ensure local responders have all the resources necessary to safely respond to this dynamic situation. 

'We are committed to a unified, whole-of-government response focused on keeping our communities safe.'

Firefighters first responded on Thursday after vapors began escaping from the massive storage tank at the company's Garden Grove facility. 

Officials said the tank's temperature had increased, activating a relief valve designed to release pressure safely. 

At first, crews believed they had stabilized the emergency after deploying cooling measures and using water systems to reduce the tank's temperature.

Evacuation orders issued on Thursday evening were briefly lifted after vapor conditions improved, but the situation dramatically deteriorated again overnight.

Multiple evacuation locations were set up outside the Garden Grove area, including Anaheim and Huntington Beach, according to the city website. 

Approximately 15 percent of people ordered to evacuate opted to stay home, reported the New York Post.

It is unclear when evacuated residents may be able to return to their homes. 

By early Friday morning, officials realized a damaged valve on the compromised tank had made it impossible to safely remove or neutralize the chemicals inside.

'We have determined that the tank that is in the biggest crisis is, in fact, unable to be secured and mitigated,' Orange County Fire Authority Division Chief Craig Covey warned during a tense emergency briefing.

'This thing is going to fail. We don't know when,' he added. 'There is a lot of anxiety over this.' 

The Orange County Fire Authority worked overnight Friday in an attempt to neutralize adjacent tanks in an effort to mitigate the threats of a major disaster. 

Orange County Representative Derek Tran said at a press conference on Saturday that the adjacent tanks were under careful watch because they contained the same toxic chemicals. 

'The additional part to all of this that complicates things is the two other tanks that are located in there,' he said. 'While those tanks are not failing, they contain 30-something thousand additional gallons of the same toxic chemicals.'

But the emergency proclamation stated that despite efforts to quell the problem 'significant risk remains of a catastrophic event that could lead to a hazardous release of dangerous chemicals.'

Tran said crews are working 24 hours a day to address the issue. 

Failures with the internal temperature gauge of the primary tank caused it to climb to 90 degrees on Saturday morning, after reading 77 degrees the day before, according to Fox Digital.

'Yesterday afternoon, I did report that we had some positive intel and that the tanks were stable, and we were keeping the temperature cool,' Covey said. 'And, actually, we thought we were reducing it a little bit.'

'Unfortunately, I have to say those temperatures we are doing is via drone, doing readings external of the vessel.'

After the failure of overnight procedures, officials developed a third outcome that could circumvent disaster. 

Crews planned to use a continuous heavy stream of water to slowly 'cure' and harden the dangerous chemicals in the affected tank from the outside.

'We are not giving up,' he said. 'We are not accepting the fact that we just have to let this thing fail. We’re going to try to find a solution.'

Responders have also coordinated efforts to divert the dangerous chemicals from entering storm drains, rivers and the ocean.

Health officials have said there are 'severe risks' if the affected tank ruptures, including the release of a toxic vapor.

Dr Regina Chinsio-Kwong of the Orange County Health Care Agency told Fox that if inhaled, the chemicals could cause severe respiratory issues.

'No matter what happens with the situation, whether the polymer just leaks out and then just hardens, or if it does explode and there is a vapor, you are all safe as long as you are out of the zone,' she said. 

The Daily Mail contacted the Governor's Office, GKN Aerospace, Garden Grove and Orange County Fire Authority Division for comment.